Final answer:
Gabbro transformed into amphibolite in the Adirondacks through regional metamorphism.
Step-by-step explanation:
In the Adirondacks, gabbro transformed into amphibolite through regional metamorphism. Regional metamorphism occurs when rocks are subjected to high pressures and temperatures over large areas. In this case, the gabbro was exposed to these conditions and underwent chemical and mineralogical changes, resulting in the formation of amphibolite.